Document Type

Article

Subject Area(s)

Chemical Engineering

Abstract

Themetal hydride (MHx) electrode is the negative electrode in oneof the most advanced secondary batteries (i.e.,nickel/metal hydride). The objectiveof this study is to obtain insight on the mechanismof the hydriding/dehydridingreaction in the battery by using the electrochemicalimpedance spectroscopy (EIS) technique. An equivalent circuit for the MHx electrodereaction is proposed. The rate capability of charge and dischargeof the MHx electrode is determined by thekinetics of thecharge-transfer reaction at the alloy surface, which is mainly representedby the EIS responses in the lowfrequency region. Transient andpseudo-steady-state analyses (cyclic voltammetry and potential vs. current density behavior)qualitativelyand quantitatively support the EIS results. EIS studies on electrodeswith (i) three types of bindingadditives, (ii) varying amounts ofactive material, and (iii) two types of alloys as activematerials demonstrate the usefulnessof this technique for developing electrodes withthe optimum composition and structure.